A new method with laser interferometry is used to enhance the traceability for sinusoidal pressure calibration in water. The laser vibrometer measures the dynamic pressure based on the acousto-optic effect. The relation of the refractive index of water and the optical path length with the pressure’s change is built based on the Lorentz–Lorenz equation, and the conversion coefficients are tested by static calibration in situ. A device with a piezoelectric transducer and resonant pressure pipe with water is set up to generate sinusoidal pressure up to 20 kHz. With the conversion coefficients, the reference sinusoidal pressure is measured by the laser interferometer for pressure sensors’ dynamic calibration. The experiment results show that under 10 kHz, the measurement results between the laser vibrometer and a piezoelectric sensor are in basic agreement and indicate that this new method and its measurement system are feasible in sinusoidal pressure calibration. Some disturbing components including small amplitude, temperature change, pressure maldistribution, and glass windows’ vibration are also analyzed, especially for the dynamic calibrations above 10 kHz.

When the satellite is in orbit, the thruster will experience drastic temperature changes (100–1000 K) under solar radiation, which will affect the rarefied gas flow state in the micro-nozzle structure of the cold gas micro-thruster. In this study, the effect of different wall temperatures on the rarefied flow and heat transfer in the micro-nozzle is investigated based on the DSMC method. The micro-nozzle structure in this paper has a micro-channel with a large length-to-diameter ratio of 10 and a micro-scale needle valve displacement (maximum needle valve displacement up to 4 μm). This leads to more pronounced multiscale flow characteristics in the micro-nozzle, which is more influenced by the change in wall temperature. At wall temperatures ranging from 100 K to 1000 K, the spatial distribution of local Kn distribution, slip velocity distribution, temperature, and wall heat flux distribution in the micro-nozzle were calculated. The slip flow region is located in the flow channel and transforms into transition flow as the slip velocity reaches approximately 50 m/s. The spatial distribution of the flow pattern is dominated by the wall temperature at small needle valve opening ratios. The higher the wall temperature, the smaller the temperature drop ratio in the low-temperature region inside the micro-nozzle. The results of the study provide a reference for the design of temperature control of micro-nozzles in cold gas micro-thrusters.

It is important to locate the impact source on composite lamination structures for the invisible damage caused by low-velocity impacts. However, desired signals of a low-velocity impact are easily overwhelmed by a strong noise in a 1-D time-domain with sparse sensor networks, reducing localization accuracy. To address this problem, a DenseNet-convolutional block attention module (CBAM) model is proposed based on image regression to realize high-precision impact localization on composite lamination structures. To reduce the interference of baseline drift and high-frequency noise components, the collected signals are reconstructed by a discrete wavelet. To highlight all the signal features in both the time and frequency domains, the reconstructed signals are transformed into a database of time-frequency spectrograms by using the short-time Fourier transform (STFT) and image augmentation methods. A 650 × 650 × 3 mm composite lamination structure is designed to validate the efficiency of our suggested method. The experiment results demonstrate that the model exhibits excellent global performance when CBAM focuses on spectrograms before the Dense-Block process. The maximum localization errors are 12.813mm for the DenseNet-CBAM model, 26.926mm for the traditional statistical method, and 13.963mm for ResNet-CBAM. The mean localization errors are 6.419mm for the DenseNet-CBAM model, 12.041mm for the traditional statistical method, and 7.873mm for ResNet-CBAM. In all, our suggested DenseNet-CBAM method is superior to traditional statistical methods and general deep learning methods.

Sinusoidal phase-modulated signal light through the interferometer can produce a beat signal. Moreover, its amplitude monotonically changes with the signal light frequency. So the beat signal amplitude can be used to measure laser-Doppler frequency shift. In addition to the beat signal, the phase-modulated signal also contains a direct current signal, and it still contains a large amount of frequency shift information, but the information is not utilized, resulting in the waste of information. In this paper, this kind of phase-modulated laser-Doppler frequency shift measurement method is improved to simultaneously utilize the useful information in the DC and beat signal for the frequency shift measurement. The specific method is to use the ratio of beat signal amplitude to DC signal amplitude to define a new parameter used in frequency shift measurement. The signal light intensity terms in DC and beat signal can be eliminated, so the improved measurement method does not need to measurement the signal light intensity, which makes its structure further simplified. By comparing the frequency change curves between the newly defined parameter and the beat signal amplitude theoretically, we find that they have the same distribution rule. In theory, by comparing the measurement sensitivity curves, it is proved that the improved phase-modulated frequency shift measurement method has higher measurement sensitivity and dynamic range than the unimproved one.